This invention relates to arrangements and methods for interfacing frame based communications traffic with a cell or packet based network.
Traditionally, two types of legacy telecommunication networks have been developed. The first type is connection oriented and is used for the transport of narrow band voice traffic, typically carried in TDM frames. Such networks comprise for example synchronous or plesiochronous networks.
Digital telecommunication systems are currently evolving from the so-called first generation of narrow band networks, which were primarily directed to the handling of voice and data traffic, to a new generation of broad band networks which can carry a full range of multimedia services. Within a typical narrow band network, traffic and control information are carried in 64 kbit/s bearer channels using time division multiplexing (TDM). Routing to establish communications channels between end users.is determined by the network nodes each of which is provided with a set of routing tables so as to set up an optimum route for each communication. A great deal of this narrow band, typically voice, traffic is transported via the synchronous digital hierarchy (SDH) or the equivalent North American SONET protocol. Further legacy systems employ the plesiochronous digital hierarchy (PDH). In such systems, digitised traffic from a large number of users is packed into virtual containers which are multiplexed up into synchronous or plesiochronous frames prior to transmission. There is thus a problem in adapting this synchronous or plesiochronous frame based bulk traffic for transport over a cell or packet based asynchronous broadband network. The second type of legacy network is connectionless in nature and is used for the transport of broad band packet or cell-based data traffic. There is currently a drive towards unified networks which provide end to end transport for both voice and data services. However, as there is a well established voice network base, network operators are naturally reluctant to replace such legacy networks. This issue has been addressed by providing broad band (asynchronous) overlay networks which interface with the established TDM networks to provide a voice and data transport functiori. At the interface between the two networks, an interface function maps TDM frames into packets or Asynchronous Transfer Mode (ATM) cells and vice-versa. ATM is of course just one example of a packet based network.
A goal of development of telecommunications networks is to realise the potential integration of real-time and non-real-time services. The key examples of these two types are voice telephony (real-time) and computer data (non-real-time). Voice telephony is served predominantly by circuit switched connection orientated networks that are arranged to deliver a guaranteed quality of service. Such networks are implemented by transport and switching systems that use a time division multiplex of circuits. Computer data is served predominantly by the Internet which uses a packet forwarding connectionless mode of operation or Internet protocol (IP), that is a workable paradigm best suited to the burstiness of traffic demand and general non-deterministic nature of this traffic type.
ATM (asynchronous transfer mode) has been designed from the outset to adapt to many different types of communications traffic. ATM is a connection orientated network mechanism, allowing dynamic bandwidth configuration and flexibility as a key advantage over circuit switched networks. ATM has adaptation layers for carrying given services over ATM transport and switches. However, the fixed length of ATM cells, while suitable to segmentation of long data packets, thereby simplifying and streamlining switching technologies, is still too large for certain compressed voice services, that suffer a cell assembly or xe2x80x98cellificationxe2x80x99 delay affecting existing network delay budgets and acceptable voice characteristics.
This issue has been addressed by the definition of Adaptation Layer 2 (AAL2). This is distinct from other ATM adaptation layers, since it de-couples voice packets from ATM cell boundaries, and provides for the multiplexing of mini-packets from several calls into a single ATM connection. This multiplex is asynchronous to the cell boundary and effectively introduces a new switching layer above the ATM layer.
Beyond the ability to switch in these adaptation layers and to interwork between them, is the requirement to trunk to legacy TDM and packet based networks. The various demands of IP and ATM adaptation layers, and the likelihood that both IP and ATM technologies will be deployed in the near term for both real-time and non-real-time services, has demonstrated a need for the integration of these technologies.
As mentioned above, a particular problem with voice traffic is that of minimising the cell assembly delay at the adaptation interface equipment in order to maintain the required quality of service. Interconnects currently used for packets within equipments are generally designed for use with fixed length packets or cells, e.g. ATM cells sometimes augmented with additional header or trailer bytes. Such an interconnect is the ATM Forum standard UTOPIA bus. The carriage in such systems of short variable length packets, e.g. AAL-2 that is commonly used for voice traffic, is possible only by padding them out to the full size with null data, and is thus inefficient of bandwidth.
An object of the invention is to minimize or to overcome the above disadvantage.
According to a first aspect of the invention, there is provided a method of interfacing communications traffic with a cell or packet based communications network, the method comprising segmenting the communications traffic into micro-packets each consisting of a payload and a header containing control information, and transmitting said payload and control information in parallel over separate serial lines.
According to another aspect of the invention, there is provided a serial interface for interfacing communications traffic with a cell or packet based communications network, the interface comprising; means for segmenting the frame based traffic into micro-packets each consisting of a payload and a header containing control information, and means for transmitting said payload and control information in parallel over separate serial lines.
According to a further aspect of the invention, there is provided an interface arranged to convey variable length voice and data information packets between processing devices in an asynchronous adaptation arrangement, wherein the voice and data information packets are conveyed in a serial manner within micro-packets whereby to obviate the use of null or padding data.
According to a further aspect of the invention, there is provided a method of conveying variable length voice and data information packets over an interface between processing devices in an asynchronous adaptation arrangement, wherein the voice and data information packets are conveyed in a serial manner within micro-packets whereby to obviate the use of null or padding data.
According to another aspect of the invention, there is provided a serial interface for interfacing communications traffic with a cell or packet based communications network, the interface comprising; a transmit unit, a receive unit, a first serial line and one or more further serial lines therebetween, wherein the transmit unit has packetising means for packing the communications traffic into micro-packets, each having a header portion containing control information and a payload portion, first serial transmission means for transmitting the payload portion of each said micro-packet over the first serial line to the receive unit, and further transmission means for transmitting the control information over the one or more further serial lines to the receive unit, and wherein the receive unit has means for receiving the transmitted payload and for relating the transmitted control information thereto.
According to a further aspect of the invention, there is provided a method of interfacing communications traffic with a cell or packet based communications network, the interface comprising; a transmit unit, a receive unit, a first serial line and one or more further serial lines therebetween, wherein the method comprises packetising the communications traffic into micro-packets, each having a header portion containing control information and a payload portion, transmitting the payload portion of each said micro-packet over the first serial link to the receive unit, and subsequently relating the transmitted payload and control information.
The arrangement and method provide a means of transmitting the payloads of ATM cells, AAL2 Common Part Sublayer (CPS) packets, IP packets or other packet types, together with necessary control information, using a common generic format between devices in an ATM/IP adaptation environment.
The interconnect by using a serial format permits a high bandwidth, typically 622 Mbit/s, of packet traffic to be transmitted using a small number of signal lines, thus facilitating multiple interconnects to be configured per device for scalability purposes. It also minimizes space on a Printed Circuit Board (PCB) taken by high pin-count devices and tracks, as well as minimizing power consumption.
The interconnect by providing a common generic format for the different types of packet associated with connection oriented or connectionless services, allows these packet types to be handled by the same devices without a multiplicity of different interconnects.
The interconnect is adapted to handle variable length packets, including very short packets and packets of which the length varies dynamically on any given channel, and so can carry AAL-2 and IP packets in a bandwidth efficient manner as for that of fixed length ATM cells.
The interconnect has a generic segmentation and reassembly (SAR) capability, in which the segments can be variable in length. This allows packets of any length including long IP packets to be carried efficiently.
The generic SAR capability together with the ability to carry very short packets or segments of packets, enables the segmentation of ATM cells and other medium length packets into very short fragments. This allows payload data buffering to be concentrated in one place whilst minimizing data storage elsewhere, enabling a memory efficient architecture for the adaptation functional circuitry to be used. It also obviates the need for padding with null information to minimize assembly delay.